US3495761A

US3495761A - Embossed kraft paper and paper bags made therefrom

Info

Publication number: US3495761A
Application number: US721725A
Authority: US
Inventors: Leslie L Turai; Paul Hoffman
Original assignee: Hudson Pulp and Paper Corp
Current assignee: Georgia Pacific LLC
Priority date: 1968-04-16
Filing date: 1968-04-16
Publication date: 1970-02-17
Anticipated expiration: 1987-02-17

Description

Feb. 17, 1970 L. L. TUR Al ET AL EMBOSSED KRAFT PAPER AND PAPER BAGS MADE THEREFROM Filed April 16. 1968 United States Patent US. Cl. 229-53 8 Claims ABSTRACT OF THE DISCLOSURE A multi-wall bag construction is disclosed where the outer ply of the bag is embossed to enhance the appearance, impart a non-skid or non-slide characteristic and improve the structure by imparting an extensibility characteristic.

This invention relates to packaging and more in particular to kraft paper bags of the multi-wall type having a special outer ply. An object of this invention is to provide packaging materials with improved external characteristics. Another object is to provide multi-wall bags having an outer ply of embossed paper which gives the bags improved characteristics. A further object is to provide for the above with an embossing which enhances the ap pearance. A further object is to provide for the above with an embossing which provides a superior non-slide or non-skid characteristic whereby the embossed outer surface will readily slide upon a smooth surface but it will not slide readily upon an identical or similar surface. A further object is to provide for the above with embossed paper which has an extensibility which gives it certain additional advantages including an ability to withstand certain abuse. These and other objects will be in part obvious and in part pointed out below.

In the field of multi-wall paper bags it is common practice to stack filled bags for storage and shipment. Stacking of filled bags is an awkward procedure, subject to much inaccuracy, so exact balance and alignment of them is impossible. The contents of each of the slightly nonaligned bags shifts due to vibration, movement, or gradual sifting, so that the bags tend to move with relation to each other and so that the stack becomes severely unbalanced, and shifts or collapses. To minimize the problem bags are chemically coated to give them a high friction outer surface, so that one bag tends not to slide in relation to another. The chemical coating, however, is undesirable for various reasons, for example, it is expensive to produce and it is detrimental to the appearance of the bags. Other methods for preventing skidding of the stacked bags have not proved satisfactory and are unduly costly.

In the field of packaging, appearance is of great importance. It is current practice to print the outer surface of bags, particularly multi-wall bags, to make them attractive, label them, and give information about their contents. However, the untreated surface of the bags is subject to smudging and it produces glare, so it is often unattractive and illegible. Other non-skid processes have decreased the attractiveness and legibility of the bags, such as non-skid coating imparting an undesirable coloration and texture to the surface. It is thus a further object of the present invention to provide an improved outer surface for multi-wall bags which has the characteristics of improving the overall appearance of the bag, rendering the printed material more visible and printing more easily readable. Further objects are providing a superior nonskid characteristic, rendering it resistant to certain damage by impact and rubbing and making the ply completely compatible with materials from which the inner plys are made.

Referring to the drawings:

FIGURE 1 is a perspective view of three multi-wall bags filled and stacked, which are of a type constituting one embodiment of the invention;

FIGURE 2 is a greatly enlarged plan view of the embossed outer ply of one of the bags of FIGURE 1;

FIGURE 3 is a somewhat schematic view illustrating the relationship of two embossed surfaces contacting each other, for example, in FIGURE 1, in the manner of the bottom surface of the top bag and the top surface of the middle bag;

FIGURE 4 is an enlarged plan view of a small portion of one of the two embossing rolls used for embossing the kraft paper for the outer plys of the bags of FIGURE 1; and,

FIGURES 5 and 6 are greatly enlarged representations of the surface contours of the embossing roll along the respective lines 5-5 and 6-6.

FIGURE 1 shows three filled bags 2 piled as they would be as a portion of a large stack of bags. In this embodiment the bags are of standard multi-wall type, except for the outer ply 4, and that is a sheet of polyethylene-coated kraft paper which has been embossed in accordance with the invention. The embossing is performed by passing the paper between a pair of identical embossing rolls, of the type used for embossing paper towels. A portion of one of the rolls is shown in FIGURE 4 in which the roll axis is horizontal, and the roll surface moves in the plane of the drawing as the sheet of kraft paper passes between the rolls. The embossed paper then passes with the other plys through the tuber to form the bags.

Referring to FIGURE 2, the embossing is a continuous pattern formed by staggered rows of embossed segments 14. Illustratively, each embossed segment is longer in the machine direction than in the cross direction; there being 7.4 embossed segments in the machine direction; and 9 embossed segments in the cross direction. Each embossed segment has at its center a somewhat elongated dome 8, and the sloping sides of that dome extend downwardly to other domes 9, which project from the opposite surface of the sheet and appear as concave surfaces or cavities in FIGURE 2. Hence, the exposed surface of the outer ply or sheet has a continuous sinusoidal curvature in all directions. The embossing is not deep and, in fact, in FIGURE 3, the depth of embossing is exaggerated somewhat. That depth is such as to give the desired coefiicient of friction between the contacting surfaces of two bags when one is piled upon another. The term coefficient of friction is used herein in the broad sense of relating the force required to move one object to the pressure on the supporting surface, for example, when the top bag of FIGURE 1 is moved from the rest position. Hence, there is taken into account the coefiicient of friction which the two surfaces would have if they were fiat, as well as the angular relationship between the contacting surfaces. In general, the displacement of the surface should not be greater than one-fifth of the spacing between adjacent domes 8. However, the total effect of the embossing upon the coefficient of friction depends upon the size, shape and spacing of the embossed segments and upon the depth of the embossing. In this embodiment, the top of each dome 8 is displaced from the central plane of the sheet a distance which is greater than the thickness of the sheet, although for thicker or greater weight sheets that displacement may be substantially of the order of the sheet thickness.

The shape of the embossed segments 14 is not critical, being determined by considerations of the type and specific characteristics of the paper and the appearance and other characteristics which are desired in the finished product. The segments 14 in the illustrative embodiment are in a regular pattern and are of one size, although those relationship-s are not essential for attaining certain objects of the invention. Also, the segments 14 upon the surface of one bag may be of different characteristics, e.g. larger, than the segments on the surface of a bag upon which it rests.

The important non-skid or non-slide characteristic is mechanical in a sense that there is an interengagement or mating of the embossed segments when one bag is placed upon another. As represented in FIGURE 3, the protruding domes 8 are shown somewhat nested into the slight cavities or pockets 22 of domes 9. There is no apparent tendency for the adjacent surfaces to be held together by a partial vacuum condition, as might occur if the embossed patterns were larger and deeper. It has been found that the bags can be readily piled and repiled and may be slid, one upon another, or upon a smooth surface without difficulty. Nevertheless, the embossing imparts a desirable tendency for one bag to stay in position upon another bag, and the piling of additional bags tends to increase the non-skid or non-slide characteristic between the surfaces of the lower bags.

It has been indicated above that the enhanced appearance of the bag is also an important aspect of the invention. To that end, the surface contour described above, which gives the desired coefficient of friction, also provides the enhanced appearance characteristic. Each dome 8 catches and reflects light, while each concave surface 9 tends to be shadowed. This is particularly evident with the coated surface and where there is printing. With an unembossed sheet or ply, the surface is somewhat mirrorlike so that the light reflections may interfere with reading the printing. However, the surface of the embossed sheet or ply tends to disperse the light so as to avoid objectionable reflections. Also, when the surface of an unembossed sheet is viewed at an angle substantially less than 90 from the surface, the printing is fiat. But the surface of the embossed sheet has a three-dimensional characteristic which materially improves the appearance and makes the large letters of the printing stand out very distinctly. The surfaces of each dome direct dispersed light so that the large letters can be seen even when viewed at a very small angle from the general plane of the surface. The overall effect of the embossing is to provide a greatly enhanced appearance, and there is also the physical change of providing improved viewing of trademark and other identifying color or printed characteristics on the bag.

In addition to the enhanced appearance and decorative characteristics and the non-skid and non-slide characteristics discussed above, the embossed outer ply 4 of each bag also has extensibility so that it stretches when subjected to tension forces. With a multi-wall bag having the outer ply embossed, and used in combination with extensible paper inner plies, the known advantages of extensible paper construction can be maintained. Hence, if the bag is dropped or impacted, the embossed outer ply, together with the extensible inner plies, will stretch and absorb the force without rupturing and the bag remains intact. The stretchability is present through the sheet and that characteristic is enhanced by the coating. The polyethylene coating acts to protect the sheet from physical damage and it also aids in reducing the damage due to wear when the bag is slid down chutes, etc. During such sliding movement the bag is supported by the rounded domes and there is minimum resistance to movement.

In the illustrative embodiment the embossed elements have been described in detail. There is a particular advantage in having a relatively small pattern; for example, a pattern having within the range of five to ten domes per inch.

It is thus seen that the invention provides a simple and inexpensive improvement in the construction of multi-wall bags having the various important advantages set forth above.

What is claimed is:

1. A multi-wall bag comprising a plurality of tubular plys including an outer ply which presents two opposite side walls upon which the filled bag may rest and which are contacted by adjacent bags when the filled bags are stacked, said outer ply being embossed throughout said side walls with an overall pattern comprising domes and cavities with a continuous curve in the transverse surface contour whereby the domes of one side wall will project into the cavities of the contacting side wall with a loose mating relationship, the exposed surfaces of said domes and cavities being at an angle to the general central plane of the ply to provide an appreciable coefficient of friction which constitutes the sole resistance to the sliding of one bag in a stack upon the bag beneath it.

2. A bag as described in claim 1 wherein the exposed surfaces of said side walls are covered with polyethylene.

3. A bag as described in claim 2 wherein said outer ply is of kraft paper and said domes and cavities project transversely from said center plane distances of the order of the thickness of the ply, and said continuous curve in the traverse surface contour is sinusoidal.

4. A bag as described in claim 3 wherein said domes are spaced from each other a distance of the order of /s to /2 inch.

5. A bag as described in claim 4 wherein said domes are somewhat oval with one dimension parallel to the central plane of the ply being greater than the dimension in the transverse direction.

6. A bag as described in claim 3 wherein said bag is filled with a product to form a fiat stackable item.

7. A bag as described in claim 3 wherein one of said side surfaces bears indicia and wherein said domes provide a three-dimensional appearance to the indicia.

8. A bag formed from kraft paper and adapted to be filled With a product to form a stackable item with top and bottom surfaces, the portions of said bag presenting said top and bottom surfaces being embossed with a rounded dome and rounded cavity, continuous curve pattern where the side walls of each dome and the adjacent cavities are at an angle to the general plane of the surface which provides an overall coefficient of friction which constitutes an appreciable resistance to the sliding of one item upon the item beneath it with the domes sliding with a relatively constant overall resistance to the surfaces, and said domes providing extensibility to the walls.

References Cited UNITED STATES PATENTS 2,917,223 12/1959 Le Bolt et al. 22953 3,224,574 12/1965 McConnell et al. 22953 3,283,992 11/1966 Hanson et al. 229-53 DAVID M. BOCKENEK, Primary Examiner US. Cl. X.R.